1. Field of the Invention
The present invention relates to a semiconductor device including an A/D converter, and particularly relates to a semiconductor device capable of testing an internal A/D converter by making the A/D converter output conversion results externally.
2. Description of the Related Art
In recent years, semiconductor devices which are so-called system-on-chips, where, for example, an A/D converter, a digital circuit for performing processing based on conversion results from the A/D converter, etc. are integrated on a single chip, have become mainstream. In some of such A/D-converter-including semiconductor devices, a mode-switching circuit is included to allow A/D conversion results to be externally output directly through a digital buffer, so that the A/D converter can be tested singly.
However, even in a semiconductor device in which highly precise A/D conversion is performed when the device is actually used, if, during a test, the influence of power supply voltage variation and of noise, occurring due to the driving of a relatively heavily-loaded test device (e.g., an LSI tester) by the digital buffer, is increased, the accuracy of the A/D conversion decreases, which may cause the test to be performed incorrectly.
In view of this, a technique has been proposed, in which a storage means is provided in a semiconductor device (e.g., an LSI) to allow high-frequency data output from the A/D converter to be temporarily stored in the semiconductor device, and, after the completion of A/D conversion, the data is read externally of the semiconductor device, whereby the influence of noise is reduced to thereby increase the accuracy of testing (see Japanese Laid-Open Publication No. 2001-166013, for example).